1. Field of the Invention
This invention relates to cracking catalyst compositions suitable for use in fluidized catalytic cracking processes to reduce the emission of sulfur oxides (SO.sub.x) in the regenerator stack gases.
2. Description of the Prior Art
Catalytic cracking is the major refinery process for the production of gasoline and distillate. About one-third of the total crude charged to United States refineries passes through the fluid catalytic cracking units. In that process fresh feed and recycle are mixed with regenerated catalyst at the bottom of the transfer line or riser reactor. During catalytic conversion, such as of high boiling hydrocarbons to lower boiling hydrocarbons, the reaction which takes place is accompanied by a number of complex side reactions, such as aromatization, polymerization, alkylation, and the like. As a result of these complex reactions, a hydrocarbonaceous deposit commonly called "coke" is laid down on the catalyst. This coke deposit deactivates the catalyst.The catalyst is then separated from the cracked products and drops to the stripper, where steam is injected to minimize the entrained hydrocarbons. The spent catalyst flows out of the stripper and is picked up with air for regeneration. In the regenerator, the carbon is burned off to restore catalyst activity. It is at this point that the sulfur in the coke is converted to SO.sub.2 and SO.sub.3 (SO.sub.x) resulting in the important ecological need to control emissions of the same.
U.S. Pat. No. 3,556,988 describes the method of making a suitable base catalyst that can be used to prepare the novel catalytic cracking compositions of this invention. The former is a commercially manufactured catalyst containing REY crystalline aluminosilicate zeolite in a matrix consisting of 57% SiO.sub.2, 2% ZrO.sub.2 and 1% Al.sub.2 O.sub.3.